1. [Field of the Invention]
The present invention relates to an apparatus for folding sheets which are sequentially carried out of an image formation apparatus such as a copier and printer and are collected as a bunch, and more specifically, to a sheet processing apparatus for pressing a folded loop of a bunch of folded sheets and performing processing so as not to open the folded sheets after discharging, an image formation apparatus provided with the sheet processing apparatus, and a method of pressing a fold of sheets.
2. [Description of the Related Art]
Generally, processing apparatuses are widely known which collate sheets carried out of an image formation apparatus, and perform staple binding or folding in the form of a booklet. Some of these processing apparatuses perform saddle stitching on the middle of sheets with staples or adhesive and fold in the form of a booklet. Such apparatuses perform processing for folding a bunch of 2 or 3 sheets up to about 30 sheets in two. However, after discharging, the folded loop portion subjected to the folding processing is open, and a collection amount of bunches of folded sheets is thereby decreased.
Therefore, for the folded loop portion of the sheets folded in two once subjected to the folding processing, processing is known to press a bunch of the sheets again from frontside and backside of the loop portion.
Japanese Unexamined Patent Publication No. 2016-11191 (corresponding Publication of US Patent Application No. 2015/0375958A1) filed by the present applicant shows an apparatus that shifts while applying narrow pressure, with paired press rollers narrowing stepwise, in the vertical direction of a folded loop along the folded loop of sheets folded in two. By this means, instead of pressing only the fold of sheets with press roller as in the conventional manner, the fold facing inward is added by the press rollers for pressing stepwise, the folding sheets folded with the fold facing inward generated in the fold of the sheets are hard to open, and the collection amount is improved.
However, even in the apparatus of above-mentioned Japanese Unexamined Patent Publication No. 2016-11191 (corresponding Publication of US Patent Application No. 2015/0375958A1), it was understood there was still room for improvement by the search of the present applicant. In other words, sheets are provided with fold lines inside by a plurality of rows of press rollers with different mutually opposed distances, and are certainly harder to open than in the conventional apparatus. However, when the number of folding sheets increases, the fold line is added to the center portion in the width direction of folding sheets, but the vicinities of end portions are not provided with the fold line so much, and it is not possible to fold reliably. When this phenomenon was analyzed, the phenomenon occurred from the fact that stiffness of sheets is strong in the center in the width direction of the folded loop of folding sheets, and is weaker as the portion nears the end portion. Further, it was also understood that the fold line is harder to add on the carrying-our side than the entry side of a plurality of press rollers with different distances. It is assumed that this phenomenon occurs from the fact that sheets are continued in the entering direction on the entry side, continuation of sheets is a little on the carrying-out side, and that stiffness of the folded sheet is weak.
The present invention was made for further improvements as described above, and it is a first object to reliably fold also end portions in the width direction of folding sheets by pressing the end portion in the width direction a plurality of times, while pressing the entire region in the width direction of a folded loop of the folding sheets.
Further, it is a second object to execute pressing the end portion in the width direction a plurality of times when necessary, in order to reliably press also the end portion in the width direction of sheets.